Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia with disturbances of carbohydrate, fat, and protein metabolism that result from defects in insulin secretion, insulin action, or both. Diabetes can present with characteristic symptoms such as thirst, polyuria, blurring of vision, chronic infections, slow wound healing, and weight loss. In its most severe forms, ketoacidosis or a non-ketotic hyperosmolar state may develop and lead to stupor, coma, and, in the absence of effective treatment, death.
Diabetes mellitus is subdivided into type 1 diabetes and type 2 diabetes. Type 1 diabetes (T1DM) results from auto-immune mediated destruction of the beta cells of the pancreas. Patients with T1DM exhibit little or no insulin secretion as manifested by low or undetectable levels of insulin or plasma C-peptide (also known in the art as “soluble C-peptide”). Type 2 diabetes (T2DM) is characterized by disorders of insulin action and insulin secretion, either of which may be the predominant feature. T2DM patients can be both insulin deficient and insulin resistant. At least initially, and often throughout their lifetime, these individuals do not need supplemental insulin treatment to survive. T2DM accounts for 90-95% of all cases of diabetes and can go undiagnosed for many years because the hyperglycemia is often not severe enough to provoke noticeable symptoms of diabetes or symptoms are simply not recognized. The majority of patients with T2DM are obese, and obesity itself may cause or aggravate insulin resistance. Many of those who are not obese by traditional weight criteria may have an increased percentage of body fat distributed predominantly in the abdominal region (visceral fat).
The symptoms of the early stages of diabetes often are not severe, not recognized, or may be absent. Consequently, hyperglycemia sufficient to cause pathological and functional changes may be present for a long time, occasionally up to ten years, before a diagnosis is made, usually by the detection of high levels of glucose in urine after overnight fasting during a routine medical work-up. The long-term effects of diabetes include progressive development of complications such as retinopathy with potential blindness, nephropathy that may lead to renal failure, neuropathy, microvascular changes, and autonomic dysfunction. People with diabetes are also at increased risk of cardiovascular, peripheral vascular, and cerebrovascular disease, as well as an increased risk of cancer. Several pathogenic processes are involved in the development of diabetes, including processes that destroy the insulin-secreting beta cells of the pancreas with consequent insulin deficiency, and changes in liver and smooth muscle cells that result in resistance to insulin uptake. The abnormalities of carbohydrate, fat, and protein metabolism are due to deficient action of insulin on target tissues resulting from insensitivity to insulin (insulin resistance) or lack of insulin (loss of beta cell function).
Over 18 million people in the United States have T2DM, and of these, about 5 million do not know they have the disease. These persons, who do not know they have the disease and who do not exhibit the classic symptoms of diabetes, present a major diagnostic and therapeutic challenge. Nearly 41 million persons in the United States are at significant risk of developing T2DM. These persons are broadly referred to as “pre-diabetic.” As intervention early in the development of diabetes can substantially affect the long-term prognosis of the disease, it is beneficial to identify individuals who are pre-diabetic, or those subjects who will become diabetic.